British police investigating the murder of Alexander Litvinenko are considering whether to travel to Germany after re-interviewing a key witness in the hunt for his alleged poisoners.

Traces of radiation have been found in Hamburg, where the witness, Dmitry Kovtun, is said to have visited before flying to London to meet Mr Litvinenko at the Millennium Hotel in Mayfair. Mr Kovtun, who is in Moscow receiving treatment for suspected radiation poisoning, met British detectives again yesterday. He reportedly told a Russian news agency that he had given "exhaustive" answers to their questions.

A team of nine Scotland Yard detectives travelled to Moscow two weeks ago to question witnesses. Some are still in Russia, and they are said to be keeping the idea of a trip to Germany "under review". They continue to liaise with the German authorities.

Detectives are still awaiting the results of the post-mortem examination on Mr Litvinenko. Preliminary results are said to show that he was given several times the lethal dose of the deadly radioactive toxin polonium-210.

Mr Litvinenko, 43, a former Russian spy, died in University College Hospital London last month. In a deathbed statement, he accused the Russian President, Vladimir Putin, of being behind his poisoning - an allegation that the Kremlin has vehemently denied.

Mr Kovtun and his business associate, Andrei Lugovoi, met Mr Litvinenko at the Millennium Hotel on 1 November, the day he fell ill. The German authorities found traces of polonium-210 at several locations in Hamburg visited by Mr Kovtun before he flew to London - including his ex-wife's apartment and the car that picked him up at the airport when he arrived from Moscow.

Mr Kovtun, Mr Lugovoi and a third associate, who was with them on 1 November, Vyacheslav Sokolenko, have denied any involvement in Mr Litvinenko's death.